1. Field of the Invention
The present invention relates to a cylinder type bistable permanent magnetic actuator, and particularly, to an actuator employed in power equipment for operating a circuit breaker or a switch.
2. Background of the Invention
Typically, a spring mechanism, a hydraulic actuator and a pneumatic actuator are used as actuators employed in power equipment. However, since such actuators require many components and should control mechanical energy for making a steering effort, they have a complicated structure and need to be repaired and maintained.
To solve such problems, an actuator employing permanent magnets and electric energy is used in the power equipment, instead of the existing mechanism. The permanent magnetic actuator is configured such that a mover thereof is held at a stroke due to magnetic energy of the permanent magnets, and electric energy is applied to a coil to move the mover to a stroke.
The permanent magnetic actuators may be categorized into a bistable type and a monostable type depending on a mechanism that the mover is held at a preset position. The bistable type permanent magnetic actuator is configured such that a mover can be held at each of both ends of a stroke due to permanent magnets, whereas the monostable type permanent magnetic actuator is configured such that a mover is held at only one of both ends of a stroke. Since the mover of the bistable type permanent magnetic actuator is held at a preset position by magnetic energy of permanent magnets upon opening or closing power equipment, it is more advantageous than the monostable type requiring for a separate maintenance mechanism, in that the bistable type can perform the closing/opening operation without a mechanical component such as a spring.
FIG. 1 shows an example of a bistable type permanent magnetic actuator according to the related art. The actuator includes an upper cylinder 10 having a groove in which a coil is to be disposed, an intermediate cylinder 12 located at a lower side of the upper cylinder 10, and a lower cylinder 14 located at a lower side of the intermediate cylinder 12. An inner cylinder 16 having a central portion in which a mover is to be inserted is installed inside the intermediate cylinder 12, and a permanent magnet 20 is installed at an upper surface of an edge of the inner cylinder 16.
Here, the mover 22 is installed to be reciprocated up and down between the upper cylinder 10 and the lower cylinder 14. Guide shafts 24 and 26 are coupled to upper surface and lower surface of the mover 22, respectively. The guide shafts 24 and 26 are inserted into guide holes formed in the respective upper and lower cylinders 10 and 14. An open spring 28 is installed at a lower portion of the guide shaft 26. The open spring 28 is configured to be compressed when the mover 22 is located at a lower side so as to upwardly apply an elastic force to the mover 12.
An upper coil 30 and a lower coil 32 are installed in the upper cylinder 10 and the lower cylinder 14, respectively.
An operation of the actuator will be described hereinafter. As shown in FIG. 1, in a state of being contacted with the lower cylinder 14, the mover 22 is held in the contacted state with the lower cylinder 14 by a magnetic flux generated by the permanent magnet 20. Under this state, upon applying a current to the upper coil 30, a magnetic force is upwardly applied to the mover 22. If the magnetic force becomes stronger, the mover 22 is moved upwardly so as to come in contact with the upper cylinder 10 as shown in FIG. 2. At this moment, the flow of the magnetic flux generated by the permanent magnet 20 is changed. Accordingly, the mover 22 is held at the upwardly moved position by the magnetic flux of the permanent magnet 20.
On the contrary, when the mover 22 is kept located at the position shown in FIG. 2 by the magnetic force of the permanent magnet, upon applying a current to the lower coil 32, a magnetic force is applied to the mover 22 downwardly. If the downwardly applied force becomes stronger than the force of the permanent magnet 20, the mover 22 is then moved downwardly so as to come in contact with the lower cylinder 14 as shown in FIG. 1. The contacted state is maintained by the magnetic force of the permanent magnet 20. The open spring 28 may apply an elastic energy to the mover, which is accordingly moved upwardly when manually opening a contact of an external power equipment in case where the actuator is connected to the power equipment (e.g., a circuit breaker or a switch).
However, the main components, i.e., upper cylinder, lower cylinder, intermediate cylinder and inner cylinder, constructing the related art actuator should be machined into the shape of hollow cylinders, thereby increasing the machining cost. Further, since the permanent magnet mounted onto the cylinder is formed in a ring shape having a large outer diameter, the cost required for fabricating the magnet is increased as well.
Besides, such components in the cylindrical shape should be assembled on the same shaft line, which causes difficulty in the assembly. Also, one permanent magnet attracts the mover. Accordingly, the magnet has a great magnetic force, so as to problematically attract other components during the assembling process.